There is a magnetic sensor that includes a magneto resistance effect (MR) element in which electrical resistance varies corresponding to an external magnetic field. One example of such a magnetic sensor is a thin film magnetic head that reads magnetic information written to a recording medium such as a hard disk.
A current in plane (CIP) element, in which a sense current flows in an in-plane direction of a film surface, and a current perpendicular to plane (CPP) element, in which a sense current flows in a direction orthogonal to a film surface, have been developed as MR elements. As the CPP element, a tunnel magneto-resistance (TMR) element to which a TMR effect is applied and a giant magneto resistance (GMR) element to which a GMR effect is applied are known.
One example of the MR element is an element including a spin-valve film (hereafter, referred to as an SV film). The SV film includes a pinned layer in which a magnetization direction is pinned with respect to an external magnetic field, a free layer in which a magnetization direction varies corresponding to an external magnetic field, and a spacer layer that is sandwiched by the pinned layer and the free layer. The SV film is sandwiched by a pair of electrode layers that supply a sense current. A resistance of the SV film varies depending on a relative angle of the magnetization direction of the pinned layer and the magnetization direction of the free layer. By detecting the variation of the resistance, the magnetic sensor measures an external magnetic field.
JP Patent Application Publication No. 2004-234755A discloses a thin film magnetic head including a resistor connected in parallel with an MR element. The resistor prevents the occurrence of electrostatic discharge (ESD) damage caused by a large current flowing in the MR element.
Specifically, the TMR element has a small breakdown voltage compared to the GMR element, and in turn ESD damage is highly likely to occur. In a magnetic sensor including the TMR element, the resistor is, in many cases, connected with the TMR element in parallel to prevent the ESD damage.
An output value of the magnetic sensor depends on a resistance of the resistor. Therefore, a resistor is produced such that a resistance is a preset value. However, the resistance of the resistor may vary because of a manufacturing process. When the resistance of the resistor varies widely, the performance of the magnetic sensor decreases.
Therefore, it is desired to examine whether the resistance is within the predefined range by measuring the resistance of the resistor after the manufacture of the magnetic sensor. However, in case the resistor is built into the magnetic sensor and is not externally exposed, it is impossible to directly measure the resistance of the resistor. Specifically, in case the TMR element and the resistor are embedded in an insulation layer like the thin film magnetic head, it is impossible to directly measure the resistance of the resistor without breaking the thin film magnetic head.
Therefore, it is desired to provide a method for measuring a resistance of a resistor connected in parallel with an MR element without breaking a magnetic sensor.